public class LinkedList {

    public class ListNode{
         int val;
         ListNode prev;
         ListNode next;

        public ListNode(int val){
            this.val = val;
        }
    }

    ListNode head = null;
    ListNode tail = null;

    //头插法
    public void addFirst(int data){
        ListNode node = new ListNode(data);
        if(head == null){
            head = node;
            tail = node;
        }else{
            node.next = head;
            head.prev = node;
            head = node;
        }
    }
    //尾插法
    public void addLast(int data){
        ListNode node = new ListNode(data);
        if(head == null){
            head = node;
            tail = node;
        }else{
            node.prev = tail;
            tail.next = node;
            tail = node;
        }
    }
    public int size(){
        int count = 0;
        ListNode cur = head;
        while (cur != null){
            count++;
            cur = cur.next;
        }
        return count;
    }
    //任意位置插入,第一个数据节点为0号下标
    public boolean addIndex(int index,int data){
        ListNode cur = head;
        ListNode node = new ListNode(data);
        if(index < 0 || index > size()){
            return false;
        } else if (index == 0) {
            addFirst(data);
            return true;
        } else if (index == size()) {
            addLast(data);
            return true;
        } else {
            if(head == null){
                return false;
            }
            while (index > 0){
                cur = cur.next;
                index--;
            }
            node.next = cur;
            node.prev = cur.prev;
            cur.prev.next = node;
            cur.prev = node;
        }
        return true;

    }
    //查找是否包含关键字key是否在单链表当中
    public boolean contains(int key){
        if(head == null){
            return false;
        }
        ListNode cur = head;
        while(cur != null){
            if(cur.val == key){
                return true;
            }
            cur = cur.next;
        }
        return false;
    }
    //删除第一次出现关键字为key的节点
    public void remove(int key){
        if(head == null){
            return;
        }
        if(head.val == key){
            head = head.next;
            head.prev = null;
            return;
        }
        if (tail.val == key){
            tail = tail.prev;
            tail.next = null;
            return;
        }
        ListNode cur = head;

        while(cur != null){
            if(cur.val == key){
                cur.prev.next = cur.next;
                cur.next.prev = cur.prev;
                return;
            }
            cur = cur.next;
        }

    }
    //删除所有值为key的节点
    public void removeAllKey(int key){
        if(head == null){
            return;
        }
        while (head.val == key) {
            head = head.next;
            if(head == null){
                tail = null;
                return;
            }
            head.prev = null;
        }
        while (tail != null && tail.val == key){
            tail = tail.prev;
            if(tail == null){
                return;
            }
            tail.next = null;
        }
        ListNode cur = head;

        while(cur != null){
            if(cur.val == key){
                cur.prev.next = cur.next;
                cur.next.prev = cur.prev;
            }
            cur = cur.next;
        }
    }
    //得到单链表的长度
    public void display(){
        ListNode cur = head;
        if(head == null){
            return;
        }
        while(cur != null){
            System.out.print(cur.val + " ");
            cur = cur.next;
        }
        System.out.println();
    }
    public void clear(){
        head = tail = null;
    }
}
